科研之友
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摘要
The K-a band radar imaging mechanism of the submerged wreck/sand ribbon of the motor vessel (M/V) Birkenfels in the southern North Sea is investigated by applying the quasi-specular scattering theory and considering the capillary as well as the gravity wave ranges of the wave energy density spectrum. For the imaging of wrecks and other oceanographic and meteorological phenomena at the sea surface it is assumed that quasi-specular scattering becomes dominant at higher radar frequencies like K-a and X band and wind speeds > 7-8 m s(-1). Multibeam echo sounder images of the Birkenfels wreck and associated sand ribbons as well as other available environmental in situ data have been analyzed. The formation of sand ribbons at the sea bed and the manifestation of its radar signatures at the water surface are caused by an elliptical vortex or helical flow cell triggered by unidirectional tidal current flow interacting with the wreck. The difference between simulated and measured normalized radar cross section (NRCS) modulation as a function of the space variable is less than 31.6%. Results are presented for NRCS simulations dependent on position for different effective incidence angles, unidirectional current speeds, wind speeds, and relaxation rates. The calculated current gradient or strain rate of the imaging theory has the same order of magnitude as those obtained for marine sand waves. This implies that the responsible hydrodynamic interaction mechanism is able to produce radar signatures of submerged wrecks/sand ribbons and make them visible at the sea surface.
- 出版日期2010-10-23
